1. Field
The present invention relates generally to an position control device. More specifically, the present invention relates to a three-dimensional ultrasonic position control device suitable for controlling computer displays or robot movements.
2. Art Background
Graphical input devices for computers such as the mouse taught in USP 4,464,652 issued to William F. Lapson et al Aug. 7, 1984 are well known in the field of display systems, and more particularly in the field of controlling cursor positions on a computer display. However, mouse systems require a flat surface on which to operate the mouse and are inherently limited to two dimensions.
Ultrasonics have been used both in continuous wave (cw) applications and in pulse mode (pm) applications to detect positions. While cw techniques are able to measure distances quite accurately, they have problems with reflections due to multipath phenomena.
Both one-way and two-way pulse mode ultrasonic position detecting devices are known. Such systems have been used extensively in underwater applications such as for tracking torpedoes. U.S. Patent 3,205,475 issued to Rene N. Foss describes such a one-way system. A transmitter is positioned on a torpedo and its position relative to orthoganally positioned hydrophones is determined. This system is based on synchronizing clocks on the torpedo transmitter with clocks on the receiver so that transit times of the ultrasonic signal from the torpedo to the hydrophones can be determined without cabling. However, this system relies on accurate synchronized clocks, pre-launch synchronization and computation of the desired coordinate positions directly from the propagation times of the pulses from the torpedo to the hydrophones.
U.S. Patent 3,421,138 issued to Pierre Moulin et al describes another underwater positioning system for locating a floating installation or a submarine. For example, a ship's location is determined by transmitting an acoustical signal from the ship, receiving the acoustical signal at fixed locations on the ocean floor, and radioing back to the ship from floating buoys in response to the detections. In the preferred embodiment, this system makes certain approximations which take advantage of the fact that in this application the "z" distance, the depth of the water, remains relatively constant.
U.S. Patent 3,821,469 issued to Albert L. Whesone et al describes a graphical data device which provides digitized three dimensional positioning information by responding to the leading edge of the air propogated shock wave generated by a spark. However this technique requires two or three distributed strip-microphone receivers and is generally limited to determining positions of a stylus within a volume bounded by the distributed receivers.
Another graphics tablet is described in U.S. Patent 4,124,838 issued to Kiss. In the disclosed system a graphics tablet has an acoustically reflective movable element, two orthoganally positioned distributed strip-microphones along the axes, and a source of periodic sound waves at the origin.
A. E. Benner and P. de Bruyne describe a sonic pen system in an article titled A Sonic Pen: A Digital Stylus System, which appeared in the IEEE Transactions on Computers, June 1970. This system is used as a two or three dimensional computer graphical input device. However this system also uses a spark transmitter and distributed strip-microphones.
An article titled "The Lincoln Wand" by Roberts et al in the 1966 Fall Joint Computer Conference AFIPS Proceedings describes a three dimensional ultrasonic input system utilizing four transmitters fixed in a square and a hand-held pen containing a single receiver. The multiple transmitters are activated in sequence, allowing for sound echoes to die out between activations, which results in an inherently long cycle time, and a relatively slow response time.
A device for measuring three dimensional coordinates of models is taught in U.S. Patent 3,924,450 issued to Uchiyama et al. In this system a computer is used to calculate the position of an end of a pointer having two transmitters fixed on the pointer at known positions relative to the end. This system calculates the position of the end in response to the propagation time of a supersonic signal from each of the transmitters to each of three detectors positioned at known coordinates and positioned so as to have unobstructed propagation paths to each of the transmitters. In effect, this provides a five-dimensional input device. Further, this disclosure does not teach any particular techniques for efficiently solving the equations involved.
Also, USP 3,792,243 describes a Method for Encoding Positions of Mechanisms, USP 3,792,424 describes Apparatus for Detecting the Position of a Movable Article Under Water, USP 3,745,519 describes a Small Craft Positioning System and USP 3,383,651 describes a Plane Coordinate Computing System.